On second thought, set aside the treats. This won’t be a happy occasion.

On that date, says the California-based Global Footprint Network, we humans will have consumed our allotment of the planet’s resources for the entire year: From then until the end of 2010, we’ll be in ecological deficit — like going into the red in personal or business finances, but with even more dire consequences.

The Earth has a limited amount of the resources humans need to survive. The important ones — fish, forests, agricultural land, water and air — can replenish or cleanse themselves.

But like taking more from a bank account than we deposit, since 1986 we’ve been over-drawing these resources — cutting too many trees; over-fishing — and creating more carbon dioxide and other wastes than the planet can absorb.

Despite pollution controls and improved energy efficiency, over the past quarter-century Overshoot Day has advanced on average 3.5 days annually. While this year’s date hasn’t been established yet, it’s expected to follow the trend.

Governments and industries don’t include ecological debt in their financial statements: It’s considered external to their operations. If it were counted, the costs of goods and services would soar.

The debt has developed at astonishing speed. Fifty years ago, Earth’s population consumed only half the planet’s potential resources and dumped just half the waste nature could handle. Now, we use at least 1.4 times what’s available. The Network predicts that even with projected efficiency gains, we’ll be taking double by the early 2030s and “reaching this level of ecological deficit spending may be physically impossible.”

The current environmental red ink would be much deeper if everyone on Earth lived like us. If global consumption equaled the average Canadian’s, Overshoot Day would have fallen on April 17 this year. Based on the American lifestyle, the deficit would have begun on March 21.

The worldwide date is later because poorer nations, from whom we buy many goods, are still in surplus. We are, in effect, in environmental debt to them, just as the entire planet is writing a green IOU to future generations.

In fact, developing countries argue the debt they’re owed by industrialized nations isn’t just an environmental issue but also a matter of social justice that demands additional reparations.

For 500 years, says Ecuador’s Accion Ecologica, “the North . . . took away whatever was valuable in the colonies and rendered the people . . . increasingly impoverished.

“The ecological debt . . . continues to be accumulated even today . . . on account of resource plundering, environmental damages, and the free occupation of environmental space to deposit wastes, such as greenhouse gases.”

We might be expected to reduce our consumption to allow those in poorer parts of the world to move closer to our lifestyle.

Climate change demonstrates the situation’s gravity. Scientists calculate humans can emit no more than 18 billion tonnes of greenhouse gases annually to maintain a reasonable level in the atmosphere. With the global population expected to reach 9 billion by 2050, per capita emissions must average two tonnes. The current figure for Canada and the U.S. is about 20 tonnes.

That’s why a small but growing band of economists argues for a zero-growth economy.

Overshoot calculations are complex; some details are open to criticism. But there’s ample evidence we’re accumulating a debt that gets harder, yet more essential, to repay.

“How can we maintain healthy economies and provide for human well-being in a way which doesn’t depend on liquidating resources and accumulating carbon dioxide?” asks Network president Mathis Wackernagel. “This will be the critical question of the 21st century.”

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